Referring to FIG. 1 of the drawings, shoes, boots, and other footwear are often made by injection molding. In this process, a mold contains a cavity that defines the outer surface of the skin of the footwear upper, and a last, which is placed in the mold, has an outer surface that defines the inner surface of the skin. The last and mold are configured such that there is a space between the mold and the last. A sock made from neoprene or a similar material is placed on a last before the last is placed in the mold. The thickness of the skin will be the width of the space between the wall of the mold cavity and the outer surface of the last, less the thickness of the sock. This sock acts as a release agent between the last and the mold. The sock becomes bonded to the thermoplastic material that is injected into the mold when the material cools and creates a lining which provides more comfort than the skin material alone would provide. With injection-molded footwear, it is desirable that the thickness of the skin be as small as possible in order to reduce the weight of the footwear and still provide the desired rigidity and strength. With the prior art method of making injection molded footwear, obtaining a thin skin is difficult, and in order to prevent the footwear from being too thin it may be necessary to make it thicker than desired. While the sock is typically quite thin, it can have enough variation in its thickness that it may not be possible to make the shoe as thin as desired without making some portions of it too thin.